The present invention relates to a method and to apparatus for monitoring coating means in an installation for die-casting metals or metal alloys.
More precisely, in an installation for die-casting metals or metal alloys, the present invention relates to apparatus for monitoring, i.e. optimizing, the spreading of a coating liquid on the inside faces of the die used for performing the casting operation.
With reference initially to accompanying FIGS. 1a to 1d, an installation of known type is described for injection casting pieces made of metal alloy. The installation essentially comprises a die 12 made up of two portions, respectively a moving portion 14 and a fixed portion 16, with portions of the inside faces thereof respectively referenced 14a and 16a defining the cavity 18 of the die. When the die is closed, the alloy to be cast is placed in a container 20 and is injected under pressure into the cavity 18 by a system of pistons 22. This is shown in FIGS. 1a and 1b.
At the end of the casting operation, the moving portion 14 of the die is moved away. To enable the casting 24 to be extracted from the portion 14 of the die, extraction rods such as 26 are slidably mounted through the portion 14 of the die. These rods are operated simultaneously by an actuator that is not shown in the figures.
In addition, in order to avoid adhesion phenomena between the casting and the two portions 14 and 16 of the die, prior to closing the two portions of the die and injecting the metal alloy, a coating operation is performed by means of a coating device 28 which serves to spray the inside faces 14a and 16a with a coating liquid that forms a release film on said faces. The device can be stationary during the spray step or it may be moved back and forth. It carries a certain number of spray nozzles. As is well known, there exist various coating substances, in particular coating substances based on solvents or coating substances that can be diluted in water. These coating substances are themselves well known. It will be understood that the problem is to match the concentration of coating substance in the solvent, whether water or oil, with the quantity of substance that needs to be sprayed prior to each casting operation. It is of great importance to optimize the coating operation since it serves to reduce the force that needs to be exerted by the ejector 26 to expel the casting from the die. It will be understood that if excessive stress is applied, then the ejectors or the castings being ejected run the risk of being damaged, which constitutes one of the major obstacles to automating die-casting.
It will therefore be understood that it is very important to be able to monitor the effectiveness of the coating operation on a continuous basis and to be able to take action quickly as soon as the coating parameters are no longer satisfactory.
Another object of the invention is to provide monitoring apparatus that makes it possible automatically to modify the composition or flow rate of the coating substance as a function of the actual casting conditions.
Yet another object of the invention is to provide apparatus that can trigger an alarm if the conditions under which a casting is ejected move outside normal operating conditions.